Perfect viewing conditions

[uklush]

Hi folks, I see the phrase perfect viewing conditions cropping up here and there, I just wondered what are the tell tale signs for perfect viewing conditions (dry, wet, warm, cold etc) or is it a case of look through the scope and see what you can see is the only way to tell?

Many thanks uklush

[Steve C]

I believe the prelude to good seeing is a run of Northerly winds & cold, I distinctly remember reading that somewhere but that's the only bit I recall, old age does that!

[iamjulian]

Not sure about weather conditions. I have only noticed it twice and both times it lasted for a short time (hours if not minutes). The last time it happened I was looking through the scope and it was as though everything was suddenly much more in focus. Instead of say 50 stars in the field of view, there were a couple of hundred, and it looked sharper. Imagine you were looking though a window that was slightly misted, then you wiped it so the glass was completely transparent. That's how I would describe the effect of "good seeing". I'll let others suggest reasons for why the atmosphere suddenly goes still as I am not sure.

[todd8137]

my method is to look at stars towards the horizon, half way to zenith, and then at zenith - look at the blinking or steadiness. Generally the more stars - the better the 'transparency', the less blinking - the better the seeing in terms of turbulance. Then take them in to account - it makes a difference on low surface brightness and/or mag DSO's.It's possible to have a good night where the seeing isn't great but the transparency is, and vice versa. The best nights will be where both are good at the same time.

1) Milky Way visible at any time of the year/month? If you cannot see our own galaxy, then you will have issues seeing others

2) Moon phase at the present time - one of the worst light pollution generators is the full moon actually - Very hard to see deep sky objects, and even some stars during the full moon

3) Cloud cover and moisture in the air - plays a part in blocking parts of the sky obviously the bane of all astronomers

4) smog and dust in the air - if your views look orange or red, (some of my photos do) then you will have issues having pristine conditions

5) if you are viewing the moon, and see "boiling" or see stars twinkling - then you have air currents due to temperature variations in the air, your scope air (inside), or roof to air temperature variations (above houses, outside your window etc) that cause turbulence affecting high magnification views. Not good seeing.

[michael.h.f.wilkinson]

The problem of light pollution aside, perfect viewing condition vary with the objects you want to see. A very transparent sky generally corresponds to more turbulence in the atmosphere (bright, twinkly stars in the winter skies, or the skies over many deserts). These situations are ideal for deep sky objects, were turbulence is less of a problem due to the low magnification which is used.

For planets, the transparency of the atmosphere is less of a problem because they have high surface brightness. A very slight haze in the atmosphere often corresponds to very stable skies, leading to ideal planetary viewing conditions.

In rare cases you get both high transparency and stable atmospheres. Unfortunately, turbulent, low-transparency skies are far more common.

[Jimmy Stix]

Great question OP! Thanks for some very useful answers guys.

[uklush]

As Jimmy says thanks for your thoughts! Im making notes